X-ray detector capable of managing charge sharing at its periphery

ABSTRACT

Disclosed herein is a detector, comprising: a plurality of pixels; a first guard ring comprising a plurality of segments, wherein the detector is configured to detect charge carriers collected by the segments; a controller configured to detect charge sharing between at least one pixel of the plurality of pixels and at least one segment of the first guard ring.

TECHNICAL FIELD

The disclosure herein relates to a detector suitable for X-ray (e.g.,X-ray fluorescence), particularly a detector that is capable ofdetecting and handling charging sharing at the periphery of thedetector.

BACKGROUND

X-ray fluorescence (XRF) is the emission of characteristic fluorescentX-rays from a material that has been excited by, for example, exposureto high-energy X-rays or gamma rays. By analyzing the fluorescent X-rayspectrum of a sample, the elements in the sample can be identifiedbecause each element has orbitals of characteristic energy. For a givenatom, the number of possible relaxations is limited. As shown in FIG.1A, when an electron on the L orbital relaxes to fill a vacancy on the Korbital (L→K), the fluorescent X-ray is called Kα. The fluorescent X-rayfrom M→K relaxation is called Kβ. As shown in FIG. 1B, the fluorescentX-ray from M→L relaxation is called Lα, and so on.

The fluorescent X-ray can be analyzed either by sorting the energies ofthe photons (energy-dispersive analysis) or by separating thewavelengths of the fluorescent X-ray (wavelength-dispersive analysis).The intensity of each characteristic energy peak is directly related tothe amount of each element in the sample.

Proportional counters or various types of solid-state detectors (PINdiode, Si(Li), Ge(Li), Silicon Drift Detector SDD) may be used in energydispersive analysis. These detectors are based on the same principle: anincoming X-ray photon ionizes a large number of detector atoms with theamount of charge carriers produced being proportional to the energy ofthe incoming X-ray photon. The charge carriers are collected and countedto determine the energy of the incoming X-ray photon and the processrepeats itself for the next incoming X-ray photon. After detection ofmany X-ray photons, a spectrum may be compiled by counting the number ofX-ray photons as a function of their energy.

Semiconductor X-ray detectors can directly convert X-ray into electricsignals. A semiconductor X-ray detector may include a semiconductorlayer that absorbs X-ray in wavelengths of interest. When an X-rayphoton is absorbed in the semiconductor layer, multiple charge carriers(e.g., electrons and holes) are generated. As used herein, the term“charge carriers,” “charges” and “carriers” are used interchangeably. Asemiconductor X-ray detector may have multiple pixels that canindependently determine the local intensity of X-ray and X-ray photonenergy. The charge carriers generated by an X-ray photon may be sweptunder an electric field into the pixels. If the charge carriersgenerated by a single X-ray photon are collected by more than one pixel,or by a guard ring adjacent to the pixel (“charge sharing”), theperformance of the semiconductor X-ray detector may be negativelyimpacted. In applications (e.g., elemental analysis) where X-ray photonenergy is determined, charge sharing is especially problematic foraccurate photon energy measurement, because the energy of an X-rayphoton is determined by the amount of electric charges it generates.

SUMMARY

Disclosed herein is a detector, comprising: a plurality of pixels,wherein the detector is configured to count numbers of X-ray photonsthat incident on each pixel of the plurality of pixels and whoseenergies fall in a plurality of bins, within a period of time; a guardring comprising a plurality of segments, wherein the detector isconfigured to detect charge carriers collected by the segments; acontroller configured to detect charge sharing between at least onepixel of the plurality of pixels and at least one segment of the guardring.

According to an embodiment, the plurality of pixels of the detector arearranged in an array.

According to an embodiment, the detector is configured to count thenumbers of the X-ray photons based on charge carriers generated by theX-ray photons and collected by the each pixel.

According to an embodiment, the guard ring of the detector encompassesthe plurality of pixels.

According to an embodiment, the controller is configured to detectcharge sharing by determining that a voltage detected from the at leastone pixel and a voltage detected from the segment start to change in asame time period.

According to an embodiment, the controller is configured to disregardone photon of the X-ray photons when the controller detects chargesharing between the at least one pixel and the at least one segment.

Disclosed herein is a method comprising: receiving an X-ray photon by apixel of a detector comprising a plurality of pixels and a guard ringcomprising a plurality of segments; detecting charge sharing between thepixel and a segment of the guard ring; with charge sharing detected,disregarding the X-ray photon; with no charge sharing detected and anenergy of the X-ray photon falls in one bin of a plurality of bins,counting the X-ray photon into a number of X-ray photons that incidenton the pixel and whose energy is in the bin.

According to an embodiment, the method further comprises: for eachpixel, determining the number of X-ray photons that incident on thepixel and whose energy is in the bin; and determining a total of thenumbers for the plurality of pixels.

Disclosed herein is a system comprising any of the detectors describedabove and an X-ray source. The system is configured to perform X-rayradiography on human chest, abdomen or human teeth.

Disclosed herein is a system comprising any of the detectors describedabove. The system is an X-ray telescope, or an X-ray microscopy, or asystem configured to perform mammography, industrial defect detection,microradiography, casting inspection, weld inspection, or digitalsubtraction angiography.

Disclosed herein is a cargo scanning or non-intrusive inspection (NII)system, comprising any of the detectors described above and an X-raysource. The cargo scanning or non-intrusive inspection (NII) system isconfigured for forming an image based on backscattered X-ray.

Disclosed herein is a cargo scanning or non-intrusive inspection (NII)system, comprising any of the detectors described above and an X-raysource. The cargo scanning or non-intrusive inspection (NII) system isconfigured to form an image using X-ray transmitted through an objectinspected.

Disclosed herein is a full-body scanner system comprising any of thedetectors described above and an X-ray source.

Disclosed herein is an X-ray computed tomography (X-ray CT) systemcomprising any of the detectors described above and an X-ray source.

Disclosed herein is an electron microscope comprising any of thedetectors described above, an electron source and an electronic opticalsystem.

BRIEF DESCRIPTION OF FIGURES

FIG. 1A and FIG. 1B schematically show mechanisms of XRF.

FIG. 2A schematically shows a cross-sectional view of a detectorsuitable for X-ray, according to an embodiment.

FIG. 2B schematically shows a detailed cross-sectional view of thedetector, according to an embodiment.

FIG. 2C schematically shows an alternative detailed cross-sectional viewof the detector, according to an embodiment.

FIG. 3A schematically shows a top view of a portion of the detector,according to an embodiment.

FIG. 3B schematically shows an array of pixels in the detector,according to an embodiment.

FIG. 4 schematically shows component diagrams of electronic systems of apixel and a segment of the guard ring of the detector, according to anembodiment.

FIG. 5A schematically shows a temporal change of the electric currentflowing through an electrode (upper curve) of a diode or an electriccontact of a resistor of an X-ray absorption layer exposed to X-ray, theelectric current caused by charge carriers generated by an X-ray photonincident on the X-ray absorption layer, and a corresponding temporalchange of the voltage of the electrode (lower curve), when no chargesharing occurs, according to an embodiment.

FIG. 5B schematically shows temporal changes of the electric currents(upper curve) flowing through an electrode of a pixel and a segment of aguard ring, the electric currents caused by charge carriers generated byan X-ray photon incident on the X-ray absorption layer, andcorresponding temporal changes of the voltages of the electrode and thesegment (lower curves), when charge sharing occurs between the pixel andthe segment.

FIG. 6 shows a flow chart for a method suitable for detecting X-raybased on a system that can detect charge sharing between a pixel and asegment of the guard ring in FIG. 4, according to an embodiment.

FIG. 7 schematically shows a system comprising the detector describedherein, suitable for medical imaging such as chest X-ray radiography,abdominal X-ray radiography, etc., according to an embodiment.

FIG. 8 schematically shows an element analyzer, according to anembodiment.

FIG. 9 schematically shows a cargo scanning or non-intrusive inspection(NII) system comprising the detector described herein, according to anembodiment.

FIG. 10 schematically shows another cargo scanning or non-intrusiveinspection (NII) system comprising the detector described herein,according to an embodiment.

FIG. 11 schematically shows a full-body scanner system comprising thedetector described herein, according to an embodiment.

FIG. 12 schematically shows an X-ray computed tomography (X-ray CT)system comprising the detector described herein, according to anembodiment

FIG. 13 schematically shows an electron microscope comprising thedetector described herein, according to an embodiment.

DETAILED DESCRIPTION

When an X-ray photon is absorbed in a semiconductor layer of an X-raydetector having a plurality of pixels arranged in an array, multiplecharge carriers (e.g., electrons and holes) are generated and may beswept under an electric field towards circuitry for measuring thesecharge carriers. The carriers drift along the direction of the electricfield and then diffuse in all directions. The envelope of carriertrajectories can be roughly a conical shape. If the envelope sits on aboundary between at least one pixel of the array and a segment of aguard ring of the X-ray detector, charge sharing occurs (“chargesharing” herein means charge carriers generated from a single X-rayphoton are collected by at least one pixel and another structure such asanother pixel or a segment of the guard ring). Charge sharing may causeinaccurate measurement of an X-ray photon energy, because the energy ofthe X-ray photon is determined by the amount of electric charges itgenerates.

In one embodiment, when charge sharing occurs between a pixel and asegment of the guard ring, the signal of the pixel may be disregarded.

FIG. 2A schematically shows a semiconductor X-ray detector 100,according to an embodiment. The semiconductor X-ray detector 100 mayinclude an X-ray absorption layer 110 and an electronics layer 120(e.g., an ASIC) for processing or analyzing electrical signals incidentX-ray generates in the X-ray absorption layer 110. The X-ray absorptionlayer 110 may include a semiconductor material such as, silicon,germanium, GaAs, CdTe, CdZnTe, or a combination thereof. Thesemiconductor may have a high mass attenuation coefficient for the X-rayenergy of interest.

As shown in a detailed cross-sectional view of the detector 100 in FIG.2B, according to an embodiment, the X-ray absorption layer 110 mayinclude one or more diodes (e.g., p-i-n or p-n) formed by a first dopedregion 111, one or more discrete regions 114 of a second doped region113. The second doped region 113 may be separated from the first dopedregion 111 by an optional the intrinsic region 112. The discreteportions 114 are separated from one another by the first doped region111 or the intrinsic region 112. The first doped region 111 and thesecond doped region 113 have opposite types of doping (e.g., region 111is p-type and region 113 is n-type, or region 111 is n-type and region113 is p-type). In the example in FIG. 2B, each of the discrete regions114 of the second doped region 113 forms a diode with the first dopedregion 111 and the optional intrinsic region 112. Namely, in the examplein FIG. 2B, the X-ray absorption layer 110 has a plurality of diodeshaving the first doped region 111 as a shared electrode. The first dopedregion 111 may also have discrete portions. In an embodiment, theplurality of diodes in the absorption layer is encompassed by one orseveral guard rings 115, wherein the guard ring adjacent to discreteregions 114 has discrete segments.

When an X-ray photon hits the X-ray absorption layer 110 includingdiodes, the X-ray photon may be absorbed and generate one or more chargecarriers by a number of mechanisms. An X-ray photon may generate 10 to100000 charge carriers. The charge carriers may drift to the electrodesof one of the diodes under an electric field. The field may be anexternal electric field. The electric contact 119B may include discreteportions each of which is in electric contact with the discrete regions114. In an embodiment, the charge carriers generated by a single X-rayphoton may be shared by one of the discrete regions 114 and a segment ofthe guard ring 115.

As shown in an alternative detailed cross-sectional view of the detector100 in FIG. 2C, according to an embodiment, the X-ray absorption layer110 may include a resistor of a semiconductor material such as, silicon,germanium, GaAs, CdTe, CdZnTe, or a combination thereof, but does notinclude a diode. The semiconductor may have a high mass attenuationcoefficient for the X-ray energy of interest.

When an X-ray photon hits the X-ray absorption layer 110 including aresistor but not diodes, it may be absorbed and generate one or morecharge carriers by a number of mechanisms. An X-ray photon may generate10 to 100000 charge carriers. The charge carriers may drift to theelectric contacts 119A and 119B under an electric field. The field maybe an external electric field. The electric contact 119B includesdiscrete portions. In an embodiment, the charge carriers generated by asingle X-ray photon may be shared by one of the discrete portions of theelectric contact 119B and a segment of the guard ring 115.

The electronics layer 120 may include an electronic system 121 and anelectronic system 122, suitable for processing or interpreting signalsgenerated by X-ray photons incident on the X-ray absorption layer 110.The electronic system 121 may include an analog circuitry such as afilter network, amplifiers, integrators, and comparators, or a digitalcircuitry such as a microprocessor, and memory. The electronic system121 may include components shared by the pixels or components dedicatedto a single pixel. For example, the electronic system 121 may include anamplifier dedicated to each pixel and a microprocessor shared among allthe pixels. The electronic system 121 may be electrically connected tothe pixels by vias 131. Space among the vias may be filled with a fillermaterial 130, which may increase the mechanical stability of theconnection of the electronics layer 120 to the X-ray absorption layer110. Other bonding techniques are possible to connect the electronicsystem 121 to the pixels without using vias.

The electronic system 122 may include an analog circuitry such as afilter network, amplifiers, integrators, and comparators, or a digitalcircuitry such as a microprocessor, and memory. The electronic system122 may include components shared by the segments or componentsdedicated to a single segment of the guard ring. For example, theelectronic system 122 may include an amplifier dedicated to each segmentand a microprocessor shared among all the segments. The electronicsystem 122 may be electrically connected to the segments of the guardring by vias 131. Space among the vias may be filled with a fillermaterial 130, which may increase the mechanical stability of theconnection of the electronics layer 120 to the X-ray absorption layer110. Other bonding techniques are possible to connect the electronicsystem 122 to the pixels without using vias.

FIG. 3A shows an exemplary top view of a portion of the device 100 withan array of discrete regions 114. Charge carriers generated by an X-rayphoton incident around the footprint of one of these discrete regions114 are not substantially shared with the segment of the guard ring. Thearea 210 around a discrete region 114 in which substantially all (morethan 95%, more than 98% or more than 99% of) charge carriers generatedby an X-ray photon incident therein flow to the discrete region 114 iscalled a pixel associated with that discrete region 114. Namely, lessthan 5%, less than 2% or less than 1% of these charge carriers flowbeyond the pixel, when the X-ray photon hits inside the pixel. Thepixels may be organized in any suitable array, such as, a square array,a triangular array and a honeycomb array. The pixels may have anysuitable shape, such as, circular, triangular, square, rectangular, andhexangular. The pixels may be individually addressable, and the pixelarray may be encompassed by one or several guard rings (such as guardrings 211 and 212). The guard ring 212 may have discrete segments.

Similarly, when the array in FIG. 3A indicates an array of discreteportions of the electric contact 119B in FIG. 2C, the charge carriersgenerated by an X-ray photon incident around the footprint of one ofthese discrete portions of the electric contact 119B are notsubstantially shared with surrounding guard rings. The area around adiscrete portion of the electric contact 119B in which substantially all(more than 95%, more than 98% or more than 99% of) charge carriersgenerated by an X-ray photon incident therein flow to the discreteportion of the electric contact 119B is called a pixel associated withthe discrete portion of the electric contact 119B. Namely, less than 5%,less than 2% or less than 1% of these charge carriers flow beyond thepixel associated with the one discrete portion of the electric contact119B, when the X-ray photon hits inside the pixel. The pixels may beorganized in any suitable array, such as, a square array, a triangulararray and a honeycomb array. The pixels may have any suitable shape,such as, circular, triangular, square, rectangular, and hexangular. Thepixels may be individually addressable, and the pixel array may beencompassed by one or several guard rings (such as guard rings 211 and212). The guard ring 212 may have discrete segments.

FIG. 3B shows an exemplary array of pixels in a semiconductor X-raydetector, according to an embodiment. When an X-ray photon hits thearray, it may be absorbed and cause multiple charge carriers to begenerated. The carriers may transport in various directions, e.g. driftalong the direction of an electric field and diffuse in all directions.In FIG. 3B, each circle (e.g. 220, 230) represents the footprint of atransport area of charge carriers generated by a photon (“transportarea” used in the present disclosure means a space the carriersgenerated by a photon are transported into).

As shown in FIG. 3B, a transport area may sit inside a pixel (e.g.transport areas 230), or on a boundary of a pixel and a segment of theguard ring (e.g. transport areas 220).

As discussed above, when a transport area sits on a boundary of a pixeland a segment of the guard ring, charge sharing occurs, which may causeissues for energy measurement. Charge sharing may also lead to errors incounting the number photons. In an embodiment, the electronic systemincluding 121 and 122 in an X-ray detector can still accurately measurethe energy of an X-ray photon even if a charge sharing occurs to thecarriers generated by the X-ray photon.

A size of a pixel can be determined by design, based on fabricationprocess. As shown in FIG. 3B, the size of each pixel is designed to bethe same and enough to cover a transport area when the correspondingphoton hits around the center of the pixel. If the size of a pixel istoo small, e.g. smaller than a transport area, then charge sharing canhappen all the time. On the other hand, if the size of a pixel is toolarge, it is very likely for multiple photons to hit the pixel at thesame time, which can generate difficulty for accurate X-ray detectionand image generation.

FIG. 4 shows component diagrams of two electronic systems of asemiconductor X-ray detector—electronic system 121 for pixels andelectronic system 122 for segments of the guard ring, according to anembodiment. In this example, as shown in FIG. 4, the electronic system121 is configured to process signals from an electrode of a diode 300 ina pixel; and the electronic system 122 configured to process signalsfrom a segment of the guard ring.

In this example, the electronic system 121 may include a capacitormodule 319, one or more sampling capacitors 316, a plurality of controlswitches 318, and a data processing module 330. As shown in FIG. 4, thecapacitor module 319 is electrically connected to the electrode of thediode 300 or the electric contact. The capacitor module 319 isconfigured to collect charge carriers from the electrode. The capacitormodule 319 can include a capacitor in the feedback path of an amplifier.The amplifier configured as such is called a capacitive transimpedanceamplifier (CTIA). CTIA has high dynamic range by keeping the amplifierfrom saturating and improves the signal-to-noise ratio by limiting thebandwidth in the signal path. Charge carriers from the electrode mayaccumulate on the capacitor over a period of time (“integration period”)(e.g., as shown in FIG. 5A, between t₀ and t₁, or between t₁ and t₂).After the integration period has expired, the capacitor voltage issampled and then reset by a reset switch 315. The capacitor module 319can include a capacitor directly connected to the electrode.

When no charge sharing occurs, the plurality of control switches 318 areclosed such that each of the one or more sampling capacitors 316 ischarged with the voltage from the front end (diode and amplifier).

As shown in FIG. 4, the electronic system 122 may include a capacitormodule 329, and a data processing module 330. The capacitor module 329is electrically connected to the segment. Like the capacitor module 319,the capacitor module 329 is configured to collect charge carriers fromthe segment. The capacitor module 329 can include a capacitor in thefeedback path of a CTIA. Charge carriers from the electrode mayaccumulate on the capacitor over a period of time (“integration period”)(e.g., as shown in FIG. 5A, between t₀ and t₁, or between t₁ and t₂).After the integration period has expired, the capacitor is reset by areset switch 325. The capacitor module 329 can include a capacitordirectly connected to the electrode.

Electronic systems 121 and 122 in FIG. 4 may comprise data processingmodules, 330 and 340 respectively, that may include downstream circuitsfor interpreting and processing signal from upstream of the electronicsystem 121 and 122.

According to an embodiment, the data processing module 330 includes afirst voltage comparator 331, a second voltage comparator 332, a counter338, a voltmeter 334 and a controller 336.

With no charge sharing, the first voltage comparator 331 is configuredto compare a voltage (e.g. a voltage of an electrode or a diode 300 ) toa first threshold. The diode may be a diode formed by the first dopedregion 111, one of the discrete regions 114 of the second doped region113, and the optional intrinsic region 112. Alternatively, the firstvoltage comparator 331 is configured to compare the voltage of anelectric contact (e.g., a discrete portion of electric contact 119B) toa first threshold. The first voltage comparator 331 may be configured tomonitor the voltage directly, or calculate the voltage by integrating anelectric current flowing through the diode or electric contact over aperiod of time. The first voltage comparator 331 may be controllablyactivated or deactivated by the controller 336. The first voltagecomparator 331 may be a continuous comparator. Namely, the first voltagecomparator 331 may be configured to be activated continuously, andmonitor the voltage continuously. The first voltage comparator 331configured as a continuous comparator reduces the chance that the system121 misses signals generated by an incident X-ray photon. The firstvoltage comparator 331 configured as a continuous comparator isespecially suitable when the incident X-ray intensity is relativelyhigh. The first voltage comparator 331 may be a clocked comparator,which has the benefit of lower power consumption. The first voltagecomparator 331 configured as a clocked comparator may cause the system121 to miss signals generated by some incident X-ray photons. When theincident X-ray intensity is low, the chance of missing an incident X-rayphoton is low because the time interval between two successive photonsis relatively long. Therefore, the first voltage comparator 331configured as a clocked comparator is especially suitable when theincident X-ray intensity is relatively low. The first threshold may be5-10%, 10%-20%, 20-30%, 30-40% or 40-50% of the maximum voltage oneincident X-ray photon may generate in the diode or the resistor. Themaximum voltage may depend on the energy of the incident X-ray photon(i.e., the wavelength of the incident X-ray), the material of the X-rayabsorption layer 110, and other factors. For example, the firstthreshold may be 50 mV, 100 mV, 150 mV, or 200 mV.

The second voltage comparator 332 is configured to compare a voltage(e.g. a voltage of an electrode or a diode 300) to a second threshold.The second voltage comparator 332 may be configured to monitor thevoltage directly, or calculate the voltage by integrating an electriccurrent flowing through the diode or the electric contact over a periodof time. The second voltage comparator 332 may be a continuouscomparator. The second voltage comparator 332 may be controllablyactivate or deactivated by the controller 336. When the second voltagecomparator 332 is deactivated, the power consumption of the secondvoltage comparator 332 may be less than 1%, less than 5%, less than 10%or less than 20% of the power consumption when the second voltagecomparator 332 is activated. The absolute value of the second thresholdis greater than the absolute value of the first threshold. As usedherein, the term “absolute value” or “modulus” |x| of a real number x isthe non-negative value of x without regard to its sign. Namely,

${x} = \left\{ {\begin{matrix}{x,{{{if}\mspace{14mu} x} \geq 0}} \\{{- x},{{{if}\mspace{14mu} x} \leq 0}}\end{matrix}.} \right.$

The second threshold may be 200%-300% of the first threshold. The secondthreshold may be at least 50% of the maximum voltage one incident X-rayphoton may generate in the diode or resistor. For example, the secondthreshold may be 100 mV, 150 mV, 200 mV, 250 mV or 300 mV. The secondvoltage comparator 332 and the first voltage comparator 331 may be thesame component. Namely, the system 121 may have one voltage comparatorthat can compare a voltage with two different thresholds at differenttimes.

The first voltage comparator 331 or the second voltage comparator 332may include one or more op-amps or any other suitable circuitry. Thefirst voltage comparator 331 or the second voltage comparator 332 mayhave a high speed to allow the system 121 to operate under a high fluxof incident X-ray.

The counter 338 is configured to register a number of X-ray photonsreaching a corresponding diode or resistor. The counter 338 may be asoftware component (e.g., a number stored in a computer memory) or ahardware component (e.g., a 4017 IC and a 7490 IC).

The controller 336 may be a hardware component such as a microcontrollerand a microprocessor. The controller 336 may be configured to start atime delay from a time at which the first voltage comparator 331determines that the absolute value of the voltage equals or exceeds theabsolute value of the first threshold (e.g., the absolute value of thevoltage increases from below the absolute value of the first thresholdto a value equal to or above the absolute value of the first threshold).The absolute value is used here because the voltage may be negative orpositive, depending on whether the voltage of the cathode or the anodeof the diode or which electric contact is used. The controller 336 maybe configured to keep deactivated the second voltage comparator 332, thecounter 338 and any other circuits the operation of the first voltagecomparator 331 does not require, before the time at which the firstvoltage comparator 331 determines that the absolute value of the voltageequals or exceeds the absolute value of the first threshold. The timedelay may expire before or after the voltage becomes stable, i.e., therate of change of the voltage is substantially zero. The phase “the rateof change of the voltage is substantially zero” means that temporalchange of the voltage is less than 0.1%/ns. The phase “the rate ofchange of the voltage is substantially non-zero” means that temporalchange of the voltage is at least 0.1%/ns.

The controller 336 may be configured to activate the second voltagecomparator during (including the beginning and the expiration) the timedelay. In an embodiment, the controller 336 is configured to activatethe second voltage comparator at the beginning of the time delay. Theterm “activate” means causing the component to enter an operationalstate (e.g., by sending a signal such as a voltage pulse or a logiclevel, by providing power, etc.). The term “deactivate” means causingthe component to enter a non-operational state (e.g., by sending asignal such as a voltage pulse or a logic level, by cut off power,etc.). The operational state may have higher power consumption (e.g., 10times higher, 100 times higher, 1000 times higher) than thenon-operational state. The controller 336 itself may be deactivateduntil the output of the first voltage comparator 331 activates thecontroller 336 when the absolute value of the voltage equals or exceedsthe absolute value of the first threshold.

The controller 336 may be configured to cause the number registered bythe counter 338 to increase by one, if, during the time delay, thesecond voltage comparator 332 determines that the absolute value of thevoltage equals or exceeds the absolute value of the second threshold.

The controller 336 may be configured to cause the voltmeter 334 tomeasure the voltage upon expiration of the time delay. The controller336 may be configured to connect the electrode to an electrical ground,so as to reset the voltage and discharge any charge carriers accumulatedon the electrode. In an embodiment, the electrode is connected to anelectrical ground after the expiration of the time delay. In anembodiment, the electrode is connected to an electrical ground for afinite reset time period. The controller 336 may connect the electrodeto the electrical ground by controlling the reset switch 315 or 325. Theswitch may be a transistor such as a field-effect transistor (FET).

In an embodiment, the system 121 has no analog filter network (e.g., aRC network). In an embodiment, the system 121 has no analog circuitry.

According to an embodiment, the data processing module 340 includes avoltage comparator 341, a voltmeter 344 and a controller 346.

The voltage comparator 341 is configured to monitor the voltage of anelectric contact (e.g., a segment of the guard ring 115). The voltagecomparator 341 may be configured to monitor the voltage directly, orcalculate the voltage by integrating an electric current flowing throughthe electric contact over a period of time. The voltage comparator 341may be controllably activated or deactivated by the controller 346. Thefirst voltage comparator 341 may be a continuous comparator. Namely, thevoltage comparator 341 may be configured to be activated continuously,and monitor the voltage continuously. The voltage comparator 341 mayalso be a clocked comparator.

When no charge sharing occurs, the two electronic systems 121 and 122may operate independently and process signals generated from theirrespective corresponding sources (a pixel or a segment of the guardring). When no charge sharing occurs on the pixel corresponding to theelectronic system 121, the plurality of control switches 318 are closedsuch that the voltage from the front end (diode and amplifier) isreflected on the sampling capacitors and measured by the data processingmodule 330. The same voltage may also be compared with a threshold bythe data processing module 330 (e.g., using the first voltage comparator331 and/or the second voltage comparator 332 ).

When no charge sharing occurs, after the rate of change of the voltagebecomes substantially zero, the voltage is proportional to the amount ofcharge carriers generated by an X-ray photon, which relates to theenergy of the X-ray photon. However, when charge sharing occurs betweenthe pixel corresponding to the electronic system 121 and a segment ofthe guard ring, the voltage measured by the electronic system 121 inFIG. 4 is not enough to estimate the accurate amount of charge carriersgenerated by the X-ray photon.

In one example, a single X-ray photon may hit on a common boundary of atleast one pixel and one segment of the guard ring, or on an area betweenthe two, and thus cause charge carriers generated and transported intothe pixel and the segment at the same time. In this case, bothelectronic systems 121 and 122 may sense a voltage increase caused by aportion of the charge carriers.

In this example, the two electronic systems 121 and 122 operate indifferent phases: phase 1 (Φ₁), and phase 3 (Φ₃). The pixel and thesegment may be in phase 1 when they are ready to detect photons. The twoelectronic systems 121 and 122 may cooperate either by communicatingdirectly to each other or by a central controller controlling all pixelsand all segments of the guard ring of the X-ray detector. Based on theircooperation, the two systems 121 and 122 can determine that chargesharing occurs on the pixels and the segment(s), e.g. when they seevoltage changes by charge carriers at the same time or in a same timeperiod.

The controller 336, in an embodiment, may be configured to disregard oneX-ray photon, then the counter 338 may not be increased, after thecharge sharing is detected.

In an embodiment, after the charge sharing is detected and the rate ofchange of the voltage is substantially zero, the controllers 336 and 346may be configured to connect the electrode to an electrical ground, soas to reset the voltage and discharge any charge carriers accumulated onthe electrodes, thus enter phase 3. The electrode is connected to anelectrical ground after the expiration of the time delay, for a finitereset time period. During phase 3, the controller 336 and 346 mayconnect the electrode to the electrical ground by controlling the resetswitch 315 and 325. The switch may be a transistor such as afield-effect transistor (FET).

After phase 3, the pixel and the segment of the guard ring may enterphase 1 again, such that they are ready to measure next incident photon.

FIG. 5A schematically shows a temporal change of the electric currentflowing through an electrode (upper curve) of a diode or an electriccontact of a resistor of an X-ray absorption layer exposed to X-ray, theelectric current caused by charge carriers generated by an X-ray photonincident on the X-ray absorption layer, and a corresponding temporalchange of the voltage of the electrode (lower curve), when no chargesharing occurs, according to an embodiment. The electrode is the diode300 as shown in FIG. 4, when no charge sharing occurs on the pixel andthe segment of the guard ring.

The voltage of the electrode may be an integral of the electric currentwith respect to time. As discussed above, a pixel is in phase 1 when itis ready to detect an X-ray photon. During phase 1, at time to, theX-ray photon hits the diode or the resistor, charge carriers start beinggenerated in the diode or the resistor, electric current starts to flowthrough the electrode of the diode or the resistor, and the absolutevalue of the voltage of the electrode or electric contact starts toincrease. At time t₁, the first voltage comparator 331 determines thatthe absolute value of the voltage equals or exceeds the absolute valueof the first threshold V1, and the controller 336 starts the time delayTD1 and the controller 336 may deactivate the first voltage comparator331 at the beginning of TD1. If the controller 336 is deactivated beforet₁, the controller 336 is activated at t₁. During TD1, the controller336 activates the second voltage comparator 332. The term “during” atime delay as used here means the beginning and the expiration (i.e.,the end) and any time in between. For example, the controller 336 mayactivate the second voltage comparator 332 at the expiration of TD1. Ifduring TD1, the second voltage comparator 332 determines that theabsolute value of the voltage equals or exceeds the absolute value ofthe second threshold V2 at time t₂, the controller 336 causes the numberregistered by the counter 338 to increase by one. At time t₂, all chargecarriers generated by the X-ray photon drift out of the X-ray absorptionlayer 110. At time t_(s), the time delay TD1 expires. In the example ofFIG. 5A, time t_(s) is after time t_(e); namely TD1 expires after allcharge carriers generated by the X-ray photon drift out of the X-rayabsorption layer 110. The rate of change of the voltage is thussubstantially zero at t_(s). The controller 336 may be configured todeactivate the second voltage comparator 332 at expiration of TD1 or att₂, or any time in between.

The controller 336 may be configured to cause the voltmeter 334 tomeasure the voltage upon expiration of the time delay TD1. In anembodiment, the controller 336 causes the voltmeter 334 to measure thevoltage after the rate of change of the voltage becomes substantiallyzero after the expiration of the time delay TD1. When no charge sharingoccurs, the voltage at this moment is proportional to the amount ofcharge carriers generated by an X-ray photon, which relates to theenergy of the X-ray photon. The controller 336 may be configured todetermine the energy of the X-ray photon based on voltage the voltmeter334 measures. One way to determine the energy is by binning the voltage.The counter 338 may have a sub-counter for each bin. When the controller336 determines that the energy of the X-ray photon falls in a bin, thecontroller 336 may cause the number registered in the sub-counter forthat bin to increase by one. Therefore, the system 121 may be able todetect an X-ray image and may be able to resolve X-ray photon energiesof each X-ray photon.

After TD1 expires, the controller 336 connects the electrode to anelectric ground for a reset period RST to allow charge carriersaccumulated on the electrode to flow to the ground and reset thevoltage. After the expiration of TD1 and before the reset period RST,the pixel may end phase 1 and enter phase 3.

After RST, the system 121 enters phase 1 again and is ready to detectanother incident X-ray photon. Implicitly, the rate of incident X-rayphotons the system 121 can handle in the example of FIG. 5A is limitedby 1/(TD1+RST). If the first voltage comparator 331 has beendeactivated, the controller 336 can activate it at any time before RSTexpires. If the controller 336 has been deactivated, it may be activatedbefore RST expires.

FIG. 5B schematically shows temporal changes of the electric currentsflowing through two electrodes, one from a pixel and one from a segmentof the guard ring (upper curves) of the X-ray absorption layer exposedto X-ray, the electric currents caused by charge carriers generated byan X-ray photon incident on the X-ray absorption layer, andcorresponding temporal changes of the voltages of electric contact ofthe pixel and the segment (lower curves), when charge sharing occurs,according to an embodiment.

The voltage of each electrode may be an integral of the correspondingelectric current with respect to time. As discussed above, the pixel andthe segment of the guard ring are in phase 1 when they are ready todetect an X-ray photon. During phase 1, at time to, the X-ray photonhits at an area near a boundary between the pixel and the segment of theguard ring, charge carriers start being generated, electric currentstarts to flow through the electric contact of the pixel and thesegment, and the absolute value of each of voltages on the electriccontact and the segment starts to increase. Then, the charge sharingbetween a pixel and a segment occurs.

According to an embodiment, the absolute values of the two voltagesstart to increase at two different times, e.g. t₀₁ and t₀₂, that arewithin a same time period. For example, the same time period may be 10μs, 1 μs, 100 ns, or 10 ns. If so, the two pixels determine that chargesharing occurs at the pixel and the segment of the guard ring.

As shown in FIG. 5B, the pixel and the segment of the guard ring mayhave different increasing rates of the voltages and/or currents, becausethe amount of transporting charge carriers may be different.

Phase 1 may end at or after the stabilization of the voltages at thepixel and the segment of the guard ring. In the example of FIG. 5B, attime t_(e), all charge carriers generated by the X-ray photon drift outof the X-ray absorption layer 110. As such, the rate of change of thevoltage at each pixel may be substantially zero after t_(e). Here, attime t^(h) after t_(e), phase 1 ends.

After the voltage is stable, the pixel and the segment of the guard ringmay enter phase 3. During phase 3, the controllers 336 and 346 connectthe electrodes to the electric ground for a reset period RST to allowcharge carriers accumulated on the electrode to flow to the ground andreset the voltage.

After RST, each of system 121 and 122 enters phase 1 again, the pixeland the segment are ready to detect another incident X-ray photon. Ifthe voltage comparator 331 or 341 has been deactivated, the controller336 or 346 can activate it at any time before RST expires. If thecontroller 336 or 346 has been deactivated, it may be activated beforeRST expires.

FIG. 6 shows a flow chart for a method suitable for detecting X-raybased on a system that can detect charge sharing between a pixel and asegment of the guard ring in FIG. 4, according to an embodiment. At 902,determine a time to at which a voltage of an electrode starts toincrease. The electrode may be a diode or an electric contact of aresistor of a pixel exposed to X-ray. At 904, compare the time to withthat of at least one segment of the guard ring. At 905, it is determinedwhether charge sharing occurs, e.g. by detecting whether the time t₀ ofthe Pixel 1 and the time to of a segment of the guard ring are within asame time period, e.g. 10 μs, 1 μs, 100 ns, or 10 ns. If charge sharingoccurs, the process moves to 916. Otherwise, if charge sharing does notoccur, the process moves to 906.

At 906, compare, e.g., using the first voltage comparator 331, anabsolute value of the voltage of an electrode of a diode or an electriccontact of a resistor exposed to X-ray, to a first threshold V1. At 907,if the absolute value of the voltage does not equal or exceed theabsolute value of the first threshold, the process goes back to step906. If the absolute value of the voltage equals or exceeds the absolutevalue of the first threshold at 907, the process continues to step 908,e.g. after a time delay or after the voltage is stabilized. At 908,compare, e.g., using the second voltage comparator 332, the absolutevalue of the voltage to a second threshold. Then, the process moves to910.

At 910, if the absolute value of the voltage does not equal or exceedthe absolute value of the second threshold, the process goes to step916. If the absolute value of the voltage or the sum voltage equals orexceeds the absolute value of the second threshold, the processcontinues to step 912. At 912, cause, e.g., using the controller 336,the number registered in the counter 338 to increase by one. At 914,determine, e.g., using the controller 336, the X-ray photon energy basedon the voltage. There may be a counter for each of the energy bins.After measuring the X-ray photon energy, the counter for the bin towhich the photon energy belongs can be increased by one. The method goesto step 916 after step 914. At 916, reset the voltage to an electricalground, e.g., by connecting the electrode of the diode or an electriccontact of a resistor to an electrical ground. After 916, the processmay go back to 902.

FIG. 7 schematically shows a system comprising the semiconductor X-raydetector 100 described herein. The system may be used for medicalimaging such as chest X-ray radiography, abdominal X-ray radiography,dental X-ray radiography, etc. The system comprises an X-ray source 701.X-ray emitted from the X-ray source 701 penetrates an object 702 (e.g.,a human body part such as chest, limb, abdomen, mouth), is attenuated bydifferent degrees by the internal structures of the object 702 (e.g.,bones, muscle, fat, organs and teeth, etc.), and is projected to thesemiconductor X-ray detector 100. The semiconductor X-ray detector 100forms an image by detecting the intensity distribution of the X-ray.

FIG. 8 schematically shows an element analyzer comprising thesemiconductor X-ray detector 100 described herein. The element analyzermeasurer is capable of detecting presence of one or more elements ofinterest on an object such as a toy. A high-energy beam of chargedparticles such as electrons or protons, or a beam of X-rays, is directedonto the object. Atoms of the objects are excited and emit X-ray atspecific wavelengths that are characteristic of the elements. The X-raydetector 100 receives the emitted X-ray and determines the presence ofthe elements based on the energy of the emitted X-ray. For example, theX-ray detector 100 may be configured to detect X-ray at wavelengths Pbwould emit. If the X-ray detector 100 actually receives X-ray from theobject at these wavelengths, it can tell that Pb is present. Thesemiconductor X-ray detector 100 described here may have otherapplications such as in an X-ray telescope, X-ray mammography,industrial X-ray defect detection, X-ray microscopy or microradiography,X-ray casting inspection, X-ray non-destructive testing, X-ray weldinspection, X-ray digital subtraction angiography, etc. It may besuitable to use this semiconductor X-ray detector 100 in place of aphotographic plate, a photographic film, a PSP plate, an X-ray imageintensifier, a scintillator, or another semiconductor X-ray detector.

FIG. 9 schematically shows a cargo scanning or non-intrusive inspection(NII) system comprising the semiconductor X-ray detector 100 describedherein. The system may be used for inspecting and identifying goods intransportation systems such as shipping containers, vehicles, ships,luggage, etc. The system comprises an X-ray source 9011. X-ray emittedfrom the X-ray source 9011 may backscatter from an object 9012 (e.g.,shipping containers, vehicles, ships, etc.) and be projected to thesemiconductor X-ray detector 100. Different internal structures of theobject 9012 may backscatter X-ray differently. The semiconductor X-raydetector 100 forms an image by detecting the intensity distribution ofthe backscattered X-ray and/or energies of the backscattered X-rayphotons.

FIG. 10 schematically shows another cargo scanning or non-intrusiveinspection (NII) system comprising the semiconductor X-ray detector 100described herein. The system may be used for luggage screening at publictransportation stations and airports. The system comprises an X-raysource 1001. X-ray emitted from the X-ray source 1001 may penetrate apiece of luggage 1002, be differently attenuated by the contents of theluggage, and projected to the semiconductor X-ray detector 100. Thesemiconductor X-ray detector 100 forms an image by detecting theintensity distribution of the transmitted X-ray. The system may revealcontents of luggage and identify items forbidden on publictransportation, such as firearms, narcotics, edged weapons, flammables.

FIG. 11 schematically shows a full-body scanner system comprising thesemiconductor X-ray detector 100 described herein. The full-body scannersystem may detect objects on a person's body for security screeningpurposes, without physically removing clothes or making physicalcontact. The full-body scanner system may be able to detect non-metalobjects. The full-body scanner system comprises an X-ray source 1101.X-ray emitted from the X-ray source 1101 may backscatter from a human1102 being screened and objects thereon, and be projected to thesemiconductor X-ray detector 100. The objects and the human body maybackscatter X-ray differently. The semiconductor X-ray detector 100forms an image by detecting the intensity distribution of thebackscattered X-ray. The semiconductor X-ray detector 100 and the X-raysource 1101 may be configured to scan the human in a linear orrotational direction.

FIG. 12 schematically shows an X-ray computed tomography (X-ray CT)system comprising the semiconductor X-ray detector 100 described herein.The X-ray CT system uses computer-processed X-rays to producetomographic images (virtual “slices”) of specific areas of a scannedobject. The tomographic images may be used for diagnostic andtherapeutic purposes in various medical disciplines, or for flawdetection, failure analysis, metrology, assembly analysis and reverseengineering. The X-ray CT system comprises the semiconductor X-raydetector 100 described herein and an X-ray source 1201. Thesemiconductor X-ray detector 100 and the X-ray source 1201 may beconfigured to rotate synchronously along one or more circular or spiralpaths.

FIG. 13 schematically shows an electron microscope comprising thesemiconductor X-ray detector 100 described herein. The electronmicroscope comprises an electron source 1301 (also called an electrongun) that is configured to emit electrons. The electron source 1301 mayhave various emission mechanisms such as thermionic, photocathode, coldemission, or plasmas source. The emitted electrons pass through anelectronic optical system 1303, which may be configured to shape,accelerate, or focus the electrons. The electrons then reach a sample1302 and an image detector may form an image therefrom. The electronmicroscope may comprise the semiconductor X-ray detector 100 describedherein, for performing energy-dispersive X-ray spectroscopy (EDS). EDSis an analytical technique used for the elemental analysis or chemicalcharacterization of a sample. When the electrons incident on a sample,they cause emission of characteristic X-rays from the sample. Theincident electrons may excite an electron in an inner shell of an atomin the sample, ejecting it from the shell while creating an electronhole where the electron was. An electron from an outer, higher-energyshell then fills the hole, and the difference in energy between thehigher-energy shell and the lower energy shell may be released in theform of an X-ray. The number and energy of the X-rays emitted from thesample can be measured by the semiconductor X-ray detector 100.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

What is claimed is:
 1. A detector, comprising: a plurality of pixels; afirst guard ring comprising a plurality of segments, wherein thedetector is configured to detect charge carriers collected by thesegments; a controller configured to detect charge sharing between atleast one pixel of the plurality of pixels and at least one segment ofthe first guard ring.
 2. The detector of claim 1, wherein the pluralityof pixels are arranged in an array.
 3. The detector of claim 1, whereinthe detector is configured to count numbers of X-ray photons thatincident on each pixel of the plurality of pixels and whose energiesfall in a plurality of bins, within a period of time, based on chargecarriers generated by the X-ray photons and collected by the each pixel.4. The detector of claim 1, wherein the first guard ring encompasses theplurality of pixels.
 5. The detector of claim 1, wherein the controlleris configured to detect charge sharing by determining that a voltagedetected from the at least one pixel and a voltage detected from thesegment start to change in a same time period.
 6. The detector of claim1, wherein the controller is configured to disregard one photon of theX-ray photons when the controller detects charge sharing between the atleast one pixel and the at least one segment.
 7. The detector of claim1, further comprising a second guard ring encompasses the first guardring.
 8. A system, comprising the detector of claim 1, and an X-raysource, wherein the system is configured for performing X-rayradiography on human body, limb, teeth.
 9. A system comprising thedetector of claim 1, and an X-ray source, wherein the system isconfigured to detect X-ray fluorescence (XRF).
 10. A system comprisingthe detector of claim 1, wherein the system is an X-ray telescope, or anX-ray microscopy, wherein the system is configured to performmammography, industrial defect detection, microradiography, castinginspection, weld inspection, or digital subtraction angiography.
 11. Acargo scanning or non-intrusive inspection (NII) system, comprising theapparatus of claim 1 and an X-ray source, wherein the cargo scanning ornon-intrusive inspection (NII) system is configured for forming an imagebased on backscattered X-ray.
 12. A cargo scanning or non-intrusiveinspection (NII) system, comprising the apparatus of claim 1 and anX-ray source, wherein the cargo scanning or non-intrusive inspection(NII) system is configured for forming an image based on X-raytransmitted through an object inspected.
 13. A full-body scanner systemcomprising the apparatus of claim 1 and an X-ray source.
 14. An X-raycomputed tomography (X-ray CT) system comprising the apparatus of claim1 and an X-ray source.
 15. An electron microscope comprising theapparatus of claim 1, an electron source and an electronic opticalsystem.